1. Field of the Invention
The present invention relates generally to clutch pistons for automatic transmissions of automobiles.
2. Related Art
Automatic transmissions in automobiles typically include one or more planetary gear sets which may be manipulated in various ways to produce a plurality of different gear ratios which may be selected for different operating conditions as programmed by a computer. The planetary gear sets are manipulated by selectively disengaging and engaging a plurality of clutch packs contained within an outer casing of the transmission. In general, each clutch pack is selectively engaged and disengaged by hydraulically actuating an associated clutch piston to energize the clutch piston against the clutch pack or withdraw the clutch piston from engagement with the clutch pack.
Typically, the clutch piston is formed of stamped steel or cast/machined aluminum with one or more rubber adjoining lips either retained within a groove or bonded directly. The rubber lip provides a fluid resistant seal between the piston assembly and the clutch housing creating a constrained cavity where fluid pressure will actuate the clutch piston in an axial direction inside the clutch housing. The rubber lip seals are typically made of a high modulus elastomer with a base polymer of FKM, AEM or ACM. The elastic nature of the rubber material allows for some distortion of the lip where the sealing contact patch is over a broader area then just the lip radius creating some resistance to movement.